A trial has opened in France to establish responsibility for a fire in the Mont Blanc tunnel which killed 39 people almost six years ago.
Lorries are now checked for overheating before entering
The 16 defendants include individuals and companies which manage the tunnel that runs between France and Italy.
They face fines and up to three years in prison if found guilty.
The fire apparently started in a truck carrying flour and margarine. The blaze trapped cars, lorries and people and burned for more than two days.
The tunnel was badly damaged and remained closed for three years.
Hundreds of people were at the courthouse for the first day of the trial - reportedly filling its 425-seat public gallery.
A spokesman for the victims' relatives, Andre Denis, told French television he hoped the trial would uncover the truth about the blaze.
"We hope to find out about the circumstances surrounding this disaster, which by all accounts could have been avoided if there had been fewer mistakes and less incompetence, and bring to light the mistakes that were made, the oversights and the negligence," he said.
The court will aim to establish whether the fire was caused by a cigarette stub, a fault in the Volvo lorry's engine or poor maintenance.
It will also examine factors such as the ventilation system and safety procedures in the tunnel, which are thought to have contributed to the disaster.
The defendants include Belgian truck driver Gilbert Degrave, the vehicle's manufacturer Volvo of Sweden, the Italian and French companies that manage the tunnel, safety regulators and Michel Charlet, mayor of the nearby town of Chamonix.
The French news agency AFP said one defendant, the former head of the ATMB French tunnel management company, Charles Salzmann, was excused from the first day because of ill-health linked to a stroke he suffered in 2003.
He is not facing charges but is required to give evidence because the disaster happened while he headed the firm.
About 160 witnesses are expected to appear.
The Italian operating company SITMB last week agreed to pay the families of victims a total of 13.5m euros ($17.5m; £9m) if 80% of the relatives accepted it as settlement.
But it says that the payment is not an acknowledgement of liability.
The trial is expected to last three months.
Presiding Judge Renaud Le Breton de Vannoise said the court would be rigorous in getting to "the truth", according to AFP.
Repairs to the 12-kilometre tunnel and the installation of new safety equipment kept it shut for more than three years.